I. Field
The present invention relates generally to communication, and more specifically to transmission mode and rate selection for a wireless communication system.
II. Background
A wireless multiple-input multiple-output (MIMO) system employs multiple (NT) transmit antennas at a transmitting entity and multiple (NR) receive antennas at a receiving entity for data transmission. A MIMO channel formed by the T transmit antennas and NR receive antennas may be decomposed into NS spatial channels, where NS≦min {NT, NR}. The NS spatial channels may be used to transmit data in parallel to achieve higher throughput and/or redundantly to achieve greater reliability.
Each spatial channel may experience various deleterious channel conditions such as, e.g., fading, multipath, and interference effects. The NS spatial channels may experience different channel conditions and may achieve different signal-to-noise-and-interference ratios (SNRs). The SNR of each spatial channel determines its transmission capacity, which is typically quantified by a particular data rate that may be reliably transmitted on the spatial channel. For a time variant MIMO channel, the channel condition changes over time and the SNR of each spatial channel also changes over time. The different SNRs for different spatial channels plus the time varying nature of the SNR for each spatial channel make it challenging to efficiently transmit data in a MIMO system.
There is therefore a need in the art for techniques to efficiently transmit data in a time-varying wireless system.